Conventionally, as such a power output apparatus, there has been proposed a vehicle-mounted power output apparatus having an engine, a planetary gear in which a carrier is connected to an output shaft of the engine and a ring gear is connected to a drive shaft, a motor MG1 connected to a sun gear of the planetary gear, and a motor MG2 selectively connected to the output shaft of the engine and the drive shaft through a clutch (for example, see Patent Document 1). According to the apparatus, at normal cruise, the motor MG2 is connected to the drive shaft so as to output a power from the engine to the drive shaft for torque conversion by functioning the motor MG1 as a generator and the motor MG2 as a motor; and when at high speed cruise, the motor MG1 is reversely rotated to function as a motor, the motor MG2 is connected to the output shaft of the engine and the motor MG2 is connected to the drive shaft for torque conversion, thereby causing the power circulation (power-electric power) which is prevented to increase the efficiency of the apparatus.    [Patent Document 1] Japanese Patent Laid-Open No. 11-332018